Nitramino and nitrosamino compounds as antifoggants for photographic emulsions



United States Patent Office 3,148,655 Patented Sept. 8, 1964 3,14%,tl66NITRAMTNQ AND NTTRAMKNO QOMPQUNDS AS ANTIFGGGANTS FQR PHGTOGRAPHKCEMULSEONS Colin Holstead, Harrow, Engiand, assignor to Eastman KodakCompany, Rochester, N.Y., a corporation of New Jersey No Brewing. FiiedJune 29, 11961, Ser. No. 129,489 17 Claims. (U. 96-10% This inventionrelates to stabilized photographic compositions, and more particularly,to photographic silver halide emulsions containing novel fog-inhibitingagents.

It is well known that photographic emulsions on storage tend to losesensitivity and to become spontaneously developable without exposure tolight. There is normally a detectable amount of the silver salt reducedduring development in the areas where no exposure was given; this iscommonly called fog, and sometimes called chemical fog where it isnecessary to distinguish between it and the effects of accidentalexposure to radiation; in this invention, we are not concerned with thelatter.

Fog depends both on the emulsion and the conditions of development; fora given emulsion it increases with the degree of development. Withconstant development conditions, it tends to increase with time,temperature and relative humidity of storage conditions; it is commonpractice to make accelerated tests of the stability of photographicemulsions by storage at increased temperature or humidity, or both. Itis of course, desirable to have emulsions as stable as possible underthe conditions of high temperature and humidity which may occur intropical climates, for example. Fog usually appears over the whole areaof the sensitive coating, but when severe, it frequently is non-uniform.Fog may also be caused by exposure to chemicals, for example, hydrogensulfide and other reactive sulfur compounds, hydrogen peroxide vapor,and strongly reducing materials. While antifoggants and stabilizers mayprotect, to some extent, against such effects, it is normally understoodthat an antifoggant protects against spontaneous growth of fog duringprolonged storage or storage at high temperatures and humidities, orduring development to maximum contrast and speed, or both.

It is an object of this invention to provide a new method forstabilizing photographic emulsions.

It is another object of this invention to inhibit fog formation inphotographic silver halide emulsions with novel addenda.

It is also an object of this invention to maintain with novelphotographic addenda the sensitivity and fog of photographic silverhalide gelatin emulsions at or close to initial optimum values under hih temperature and high humidity keeping conditions.

These and other objects of the invention are accomplished byincorporating into photographic silver halide emulsions nitraminocompounds containing the group NHNO or nitrosamino compounds containingthe group NHNO. The emulsion addenda of the invention can be representedby the formulas XNHNO and XNHNO wherein X is an organic radical andtypically can be such groups as p-toluenesulfonyl, imidazolyl,thiadiazolyl, tetrazaindenyl, triazolyl, thiazolyl, pyrimidinyl,thiazolsulfonyl, guanidino and the like groups, and includingsubstituted derivatives thereof, as well as such hydrocarbon groups asalkyl groups of 1 to 20 carbon atoms including methyl, n-propyl,Z-ethylhexyl, n-decyl, stearyl, n-eicosyl and the like groups.

The addenda of the invention described above can be added tophotographic silver halide emulsions for purposes of increasing thestability thereof. More specifically the subject addenda serve asemulsion antifoggants. Many antifoggant addenda cause substantialdesensitization or loss in speed of the emulsion when employed thereinin antifoggant amounts. However, with the subject addenda there is nosubstantial loss of speed imparted to emulsions. In many instances withthe subject addenda there is actually imparted to emulsions an increasein sensitivity or speed, this being illustrated by the data set out inthe detailed examples and tables hereinafter. It is known in the artthat the addition of compounds containing -NO moieties to photographicsilver halide emulsions is generally to be avoided as such compoundsusually have substantial desensitizing effects. Hence, it is theexception when a compound or class of compounds is found that contain NOmoieties and do not substantially desensitize photographic silver halideemulsions. The compounds of the invention contain not only a NO or -NOmoiety but also a -NH moiety to form the active nitramino (NHNO andnitrosamino groups, these two groups containing amino and nitro ornitroso moieties which cooperate to lend to compounds containing suchthe improved properties described herein.

The preparation of photographic silver halide emulsions such as aresuitably stabilized with the addenda of the invention typically involvesthree separate operations: (1) emulsification and digestion of silverhalide, (2) the freeing of the emulsion of excess water-soluble salts,suitably by washing with water, and (3) the second digestion orafter-ripening to obtain increased emulsion speed or sensitivity. (Mees,The Theory of the Photographic Process, 1954.) The stabilizers of ourinvention can be added to the emulsion before the final digestion orafterripening, or they can be added immediately prior to the coating.

The particular quantity of the present stabilizers used in a givenemulsion can vary, depending upon the effects desired, degree ofripening, silver content of the emulsion, etc. We have found thatgenerally from about .001 to 10 grams per mole of silver halide arequite adequate to accomplish the desired stabilization. Exposure of thetreated emulsion in conventional photographic testing apparatus, such asan intensity scale sensitometer, will reveal the most advantageousconcentrations for the present stabilizers in that particular emulsion.Such techniques are well understood by those skilled in the art.

The addenda of the invention can be added to photographic emulsionsusing any of the well-known techniques in emulsion making. For example,they can be dissolved in a suitable solvent and added to the silverhalide emulsion, or they can be added to the emulsion in the form of adispersion similar to the technique used to incorporate certain types ofcolor-forming compounds (couplers) in a photographic emulsion.Techniques of this type are described in Jelley et al. US. Patent2,322,027, issued June 15, 1943, and Fierke et al. US. Patent 2,801,171,issued July 30, 1957. The solvent should be selected so that it has noharmful effect upon the emulsion in accordance with usual practice, andgenerally solvents or diluents which are miscible with water are to bepreferred. Water alone is a dispersing medium for some of thestabilizers of the invention. In other cases, the subject stabilizerscan be dissolved in solvents, such as ethanol, acetone, pyridine,N,N-dimethylformamide, etc., and added to the emulsion in this form.

The emulsions of the invention can be chemically sensitized by any ofthe other well-known procedures. The

emulsions can be digested with naturally active gelatin, or sulfurcompounds can he added, such as those described in Sheppard US. Patent1,574,944, issued March 2, 1926, and Sheppard et al. 1,623,499, issuedApril 5, 1927, and Sheppard and Brigham US Patent 2,410,689, issuedNovember 5, 1946. The emulsions can also be treated with salts of thenoble metals such as ruthenium, rhodium, palladium, iridium andplatinum. Representative compound are ammonium chloropalladate,potassium chloroplatinate, and sodium chloropalladite, which are usedfor sensitizing in amounts below that which produces any substantial foginhibition, as described in Smith and Trivelli US' Patent 2,448,060,issued August 31, 1948, and as antifoggants in higher amounts, asdescribed in Trivelli and Smith US. Patents 2,566,245, issued August 28,1951 and 2,566,263, issued August 28, 1951. The emulsions can alsocontain sensitizing amounts of gold salts as described in Waller et al.US. Patent 2,399,083, issued April 23, 1946, or stabilizing amounts ofgold salts as described in Damschroder US. Patent 2,597,856, issued May27, 1952, and Yutzy and Leermakers US. Patent 2,597,915, issued May 27,1952. Suitable compounds are potassium chloroaurite, potassiumaurithiocyanate, potassium chloroaurate, auric trichloride andZ-aurosulfobenzothiazole methochloride. The emulsions can also containsensitizing amounts of reducing agents such as stannous salts (CarrollUS. Patent 2,487,850, issued November 15, 1949), polyamines, such asdiethylene triamine (Lowe and Jones US. Patent 2,518,698, issued August15, 1950), polyamines, such as spermine (Lowe and Allen US. Patent2,521,295, issued September 12, 1950), or bis(,8-aminoethyl)sulfide andits watersoluble salts (Lowe and Jones US. Patent 2,521,926, issuedSeptember 12, 1950).

The emulsions can also be optically sensitized with cyanine andmerocyanine dyes, such as those described in Brooker US. Patents1,846,301, issued February 23, 1932; 1,846,302, issued February 23,1932; and 1,942,854, issued January 9, 1934; White US. Patent 1,990,507,issued February 12, 1935; Brooker and White US. Patents 2,112,140,issued March 22, 1938; 2,165,338, issued July 11, 1939; 2,493,747,issued January 10, 1950; and 2,739,964, issued March 27, 1956; Brookerand Keyes US. Patent 2,493,748, issued January 10, 1950; Sprague US.Patents 2,503,776, issued April 11, 1950 and 2,519,001, issued August15, 1950; Heseltine and Brooker US. Patent 2,666,761, issued January 19,1954;

Heseltine US. Patent 2,734,900, issued February 14,

1956; Van Lare US. Patent 2,739,149, issued March 20, 1956; and KodakLimited British Patent 450,958, accepted July 15, 1939.

The emulsions can also contain speed-increasing compounds of thequaternary ammonium type of Carroll US. Patent 2,271,623, issuedFebruary 3, 1942; Carroll and Allen US. Patent 2,288,226, issued June30, 1942; and Carroll and Spence U.S. Patent 2,334,864, issued November23, 1943; and the polyethylene glycol type of Carroll and Beach US.Patent 2,708,162, issued May 10, 1955.

The emulsions can contain a suitable gelatin plasticizer such asglycerin; a dihydroxy alkane such as 1,5- pentane diol as described inMilton and Murray US. Patent 2, 960,404, issued November 15, 1960; anester of an ethylene bis-glycolic acid such as ethylene bis- (methylglycolate) as described in Milton US. Patent 2,904,434, issued September15, 1959; his (ethoxy diethylene glycol) succinate as described in GrayUS. Patent 2,940,854, issued June 14, 1960, or a polymeric hydrosol asresults from the emulsion polymerization of a mixture of an amide of anacid of the acrylic acid series, an acrylic acid ester and astyrene-type compound as described in Tong US. Patent 2,852,386, issuedSeptember 16, 1958. The plasticizer may be added to the emulsion beforeor after the addition of a sensitizing dye, if used.

The emulsion can be hardened with any suitable hardener for gelatin suchas formaldehyde; a halogen-substituted aliphatic acid such as mucobromicacid as described in White U. S. Patent 2,080,019, issued May 11, 1937;a compound having a plurality of acid anhydride groups such as7,8-diphenylbicyclo(2,2,2)-7-octene-2,3,- 5,6-tetracarboxylicdianhydride, or a dicarboxylic or a disulfonic acid chloride such asterephthaloyl chloride or naphthalene-1,5-disulfonyl chloride asdescribed in Allen and Carroll US. Patents 2,725,294 and 2,725,295, bothissued November 29, 1955; a cyclic 1,2-diketone such ascyclopentane-1,2-dione as described in Allen and Byers US. Patent2,725,305, issued November 29, 1955; a hisester of methane-sulfonic acidsuch as 1,2-di-(rnethanesulfonoxy)ethane as described in Allen andLaakso US. Patent 2,726,162, issued December 6, 1955;1,3-dihyr0xymethylbenzimidazol-2-one as described in July, Knott andPollak US. Patent 2,732,316, issued January 24, 1956; a dialdehyde or asodium bisulfite derivative thereof, the aldehyde groups of which areseparated by 2-3 carbon atoms, such as fl-methylglutaraldehyde bissodiumbisulfite; a bisaziridine carboxamide such as trimethylenebis(l-aziridine carboxamide) as described in Allen and Webster US.Patent 2,950,197, issued August 23, 1960; or 2,3-dihydroxy dioxane asdescribed in Jeilreys US. Patent 2,807,013, issued January 20, 1959.

The emulsion can contain a coating aid such as saponin; a lauryl oroleoyl monoether of polyethylene glycol as described in Knox and DavisU.S. Patent 2,831,766, issued April 22, 1958; a salt of a sulfated andalkylated polyethylene glycol ether as described in Knox and Davis US.Patent 2,719,087, issued September 27, 1955; an acylated alkyl taurinesuch as the sodium salt of N-oleoyl- N-methyl taurine as described inKnox, Twardokus and Davis US. Patent 2,739,891, issued March 27, 1956;the

H reaction product of a dianhydride of tetracarboxybutane with analcohol or an aliphatic amine containing from S to 18 carbon atoms whichis treated with a base, for example, the sodium salt of the monoester oftetracarboxybutane as described in Knox, Stenberg and Wilson US. Patent2,843,487, issued July 15, 1958; a watersoluble maleopimarate or amixture of a watersoluble maleopimarate and a substituted glutamate saltas described in Knox and Fowler US. Patent 2,823,123, issued February11, 1958; an alkali metal salt of a substituted amino acid such asdisodium N-(carbo-p-tert. octylphenoxypentaethoxy) glutamate, or asulfosuccinamate such as tetrasodium N-(1,2-dicarboxyethyl)-N-octadecylsulfosuccinamate, or N-lauryl disodium sulfosuccinamate.

The stabilizer addenda of the invention can be used in various kinds ofphotographic emulsions. In addition to being useful in orthochromatic,panchromatic, and infrared sensitive emulsions, they are also useful inX-ray and other non-optically sensitized emulsions. They can be added tothe emulsion before or after any optical sensitizing dyes which may beused. Various silver salts can be used as the sensitive salt such assilver bromide, silver iodide, silver chloride, or mixed silver halidessuch as silver chlorobromide, or silver bromoiodide. The subject addendacan be used in emulsions intended for color photography, for example,emulsions containing colorforming couplers or emulsions to be developedby solutions containing couplers or other color-generating materials,emulsions of the mixed-packet type, such as described in Godowsky US.Patent 2,698,794, issued J anuary 4, 1955, or emulsions of themixed-grain type, such as described in Carroll and Hanson US. Patent2,592,243, issued April 8, 1952. The subject stabilizers can also beused in emulsions which form latent images predominantly on the surfaceof the silver halide crystal or in emulsions which form latent imagespredominantly inside the silver halide crystal, such as those describedin Davey and Knott US. Patent 2,592,250, issued April 8, 1952.

The subject addenda can also be used in emulsions intended for use indiffusion transfer processes which utilize the undeveloped silver halidein the non-image areas of the negative to form a positive by dissolvingthe undeveloped silver halide and precipitating it on a receiving layerin close proximity to the original silver halide emulsion layer. Suchprocesses are described in Rott U.S. Patent 2,352,014, issued June 20,1944, and Land U.S. Patents 2,584,029, issued January 29, 1952;2,608,236, issued December 28, 1954, and 2,543,181, issued February 27,1951. They can also be used in color transfer processes which utilizethe diffusion transfer of an imagewise distribution of developer,coupler or dye, from a lightsensitive layer to a second layer, while thetwo layers are in close proximity to one another. Color processes ofthis type are described in Land U.S. Patents 2,559,643, issued July 10,1951, and 2,698,798, issued January 4, 1955; Land and Rogers BelgianPatents 554,933 and 554,934, granted August 12, 1957; InternationalPolaroid Belgian Patents 554,212, granted July 16, 1957, and 554,935,granted August 12, 1957; and Yutzy U.S. Patent 2,756,142, issued July24, 1956.

In the preparation of the silver halide dispersions employed forpreparing silver halide emulsions, there can be employed as thedispersing agent for the silver halide in its preparation, gelatin orsome other colloidal material such as colloidal albumin, a cellulosederivative, or a synthetic resin, for instance, a polyvinyl compound,although gelatin is preferred. Some colloids which can be used arepolyvinyl alcohol or a hydrolyzed polyvinyl acetate as described in LoweU.S. Patent 2,286,215, issued June 16, 1942; a far hydrolyzed celluloseester such as cellulose acetate hydrolyzed to an acetyl content of 1926%as described in U.S. Patent 2,327,808 of Lowe and Clark, issued August24, 1943; a Water-soluble ethanolamine cellulose acetate as described inYutzy U.S. Patent 2,322,085, issued June 15, 1943; a polyacrylamidehaving a combined acrylamide content of 30-60% and a specific viscosityof 0.'251.5 on an imidized polyacrylamide of like acrylamide content andviscosity as described in Lowe, Minsk and Kenyon U.S. Patent 2,541,474,issued February 13, 1951; zein as described in Lowe U.S. Patent2,563,791, issued August 7, 1951; a vinyl alcohol polymer containingurethane carboxylic acid groups of the type described in Unruh and SmithU.S. Patent 2,768,154, issued October 23, 1956; or containingcyano-acetyl groups such as the vinyl alcohol-vinyl cyanoacetatecopolymer as described in Unruh, Smith and Priest U.S. Patent 2,808,331,issued October 1, 1957; or a polymeric material which results frompolymerizing a protein or a saturated acylated protein with a monomerhaving a vinyl group as described in Illingsworth, Dann and Gates U.S.Patent 2,852,382, issued September 19, 1958. If desired, compatiblemixtures of two or more of these colloids can be employed for dispersingthe silver halide in its preparation.

The above-described emulsions of the invention can be coated on a widevariety of supports in accordance with usual practice. Typical supportsfor photographic elements of the invention include cellulose nitratefilm, cellulose acetate film, polyvinyl acetal film, polystyrene film,polyethyleneterephthalate film and related films of resinous materials,as well as glass, paper, metals, wood and others.

Several nitramino and nitrosamino derivatives of the invention wereprepared and incorporated into photographic silver halide emulsions atvarying concentrations and thereafter tested an antifoggants. Thestructural formulas of these prepared addenda of the invention arelettered and listed below, the letters given the addenda below beingused for purposes of convenience of reference to indicate these addendain the tables and examples hereinafter.

Compound A:

N -nitro-pto1uenesulphonamide I| I O 2 2N I C-NHNOz C r-N1-nitr0-2-nitramino-M-imidazoline Compound C:

Compound B:

CH SCN I l lNHNO S 3 methylthio-5-nitrosamino-1,2,4-thiadiazole CompoundD:

CH O-N l (J-NHNOz S 3-methyl5-nitramino-1,2,4-thiadiaz0le Compound E:

6-methy14-nitramino'-1,3,3a,7-tetrazaindene Compound F:

C HaC-N N lNHNOz 3-methyl-5-nitramino-1,2,4-triazole Compound G:

C HN I I NHNO 2 5-nitramino-1,2,4-thiadiaz0le Compound H:

N H CH,('l-NHNH-l-NHNO2 1acetamid0-S-nitroguanidine Compound I NH NH2-(lNHNH 1NHN0a 1-carbamoyll-nitroaminoguanidine Compound K:

C HN lH )NHN O2 2-nitramino thiazole Compound L:

4-11ydroxy-6-methyl-2-nitramino1,3,3a,7-tetrazaindene4-hydroxy-6-methyl-2-nitraminopyrimidine 7 Compound N:

OH (ISO2NHNO2 l\H-N 3- (N-nitrosulphamoyl) -1,2,4-t1-iaz01e EXAMPLE 1Typical stabilizers of the invention were incorporated into high speednegative-type gelatino-bromoiodide emulsions which were sulphur and goldsensitized and panchromatically sensitized with a cyanine dye. Thesilver halide comprised 6.2% by weight of the prepared photographicemulsions and was 95% by weight silver bromide and 5% by weight silveriodide. The emulsions were coated on cellulose acetate film supports.The prepared photographic elements were then incubated for 3 days at 120F. and 94% relative humidity and for 7 days at 120 F. and 42% relativehumidity, and then exposed in the form of film strips in an Eastman TypeIb sensitometer, developed for five minutes at 68 F., and then fixed,washed and dried in the usual manner. Test samples were also exposeddirectly after coating in the sensitometer for purposes of comparison.The developer had the following formula:

G. N-methyl-p-aminophenol sulfate 2.2 Hydroquinone 8.8 Sodium sulfite72.0 Sodium carbonate 130.0 Potassium bromide 4.0

Water to make one liter.

The results of the sensitometric tests are summarized by the data setout in Table A below with respect to the relative speed and fog for thevarious samples. In Table A the speeds indicated are a function of theexposure necessary to give a density of 0.2 above background fog, theinitial control speed being taken as 100 in each case; and theconcentrations of addenda are indicated as grams of addenda per mole ofsilver halide.

Table A 3 days 7 days Cone. of Initial test 120 F.. 120 F., Addendaaddenda 94% R11. 42% R11.

(grams/ mole of AgX) Speed Fog Speed Fog Speed Fog 0 100 11 70 2 1 0. 9100 09 (i0 19 0 100 15 40 40 0. 9 105 12 65 25 0 100 15 65 36 0. 45 10511 85 20 0. 9 100 11 65 15 1. 35 85 11 85 13 0 100 13 65 40 0. 9 100 1270 31 0 100 17 70 80 0. 9 115 13 100 36 0 100 16 45 38 0. 9 105 13 65 220 100 00 65 23 0. 9 105 70 21 Control 0 100 16 45 39 Compound G 4. 5 9014 65 18 0 100 13 50 17 0. 9 110 ll 75 40 0 100 18 65 67 1. 5 100 13 8051 0 100 21 80 34 0. 9 110 19 90 23 1. 8 100 21 80 22 0 100 21 80 34 0.9 110 95 28 0 100 21 BO 34 Compound N O. 9 110 18 100 26 D0 1. 8 100 .17100 23 EXAMPLE 2 Samples of the photographic emulsion described inExample 1 were tested with antifoggants of the invention as described inExample 1 except that the samples were stored for 3 and 6 month periodsunder ambient conditions of'about'68 F. and 50% relative humidity. Theresults of the sensitometric tests are summarized by the data set out inTable B below.

Table B Cone. of Initial 3 Months 6 Months addenda test after coatingaiter coating Addenda (grarus/ mole of .AgX) Speed Fog Speed Fog SpeedFog 0 100 .17 9O .24 .28 0. 9 115 13 105 16 100 18 0 100 16 85 14 80 184. 5 14 11 85 1O 0 18 9O 7 .21 80 .27 4. 5 100 13 100 17 90 23 0 100 1685 18 80 19 0.9 15 100 16 95 .16 01 0 100 .23 80 .25 70 .27 Compound K0. 9 18 100 16 90 18 Do. 2. 25 110 .18 100 17 100 17 As can be observedfrom the data set out in Tables A and B above, the nitramino andnitrosarnino compounds of the invention impart substantial antifoggantor stabilizing properties to photographic silver halide emulsions. Alsoto be noted is that there is no accompanying substantial loss of speedwith the improved stability in the present instance, and which loss ofspeed characterizes many stabilizers. In many instances with the subjectstabilizers there is actually an increase in speed over the controlsample containing no addenda.

The addenda of the invention can be readily prepared. Compound A wasprepared by the method of Gillibrand and Lamberton, J.C.S., 1949, 1883.Compound B was prepared by the method of McKay and Wright, J.A.C.S., 70,3990 (1948). Compound C was prepared by the method of Goerdeler andLinden, Ber. 89, 2742 (1956). Compounds F and H were prepared by themethod of Henry, J.A.C.S. 72, 5343 (1950). Compound K was prepared bythe method of Dickey, Towne and Wright, J. Org. Chem. 20, 499 (1955).The other addenda specifically referred to above were prepared by themethods described below.

Compound D.-A solution of 2.3 g. (.02 mole) of 5-amino-B-methyl-1,2,4-thiadiazole in 10 g. of 98% sulphuric acid wastreated with 1.76 mls. (.04 mole) of 95% nitric acid at 0 C. and themixture allowed to rise to room temperature. After 1% hours at roomtemperature the mixture was poured onto ice and the colorlessprecipitate filtered and washed with water. One crystallization fromwater gave 2.3 g. pure material, M.P. 210 C. with decomposition.

Compound E.Amino 6 methyl 1,3,3a,7 tetrazaindene (3.0 g., .02 mole) wasadded at 0 C. to a mixture of 15 mls. of acetic anhydride and 0.84 mls.(.02 mole) of 100% nitric acid. To this mixture was gradually added 2.5g. (0.0185 mole) of zinc chloride dissolved in 10 mls. of aceticanhydride, keeping the temperature at 15-20" C. After a further 45minutes at 20 C. the mixture was poured into water and filtered. Theproduct was dissolved in sodium bicarbonate, treated with activatedcharcoal, filtered and acidified to give a colorless material, M.P. 227C., decomposes. One crystallization from water gave pure material, M.P.229 C. decomposes.

Compound G.-5 amino 1,2,4 thiadiazole nitrate (6.6 g.) was graduallyadded, with stirring, to 20 g. of 98% sulphuric acid at 0-40 C. and themixture allowed to rise to 20 C. After 30 minutes at 20 C. the mixturewas poured onto ice and the precipitate collected. The product wascrystallized from water, with carbon treatment, to give a colorlessmaterial, 2.4 g., M.P. 207-208 C. decomposes.

Compound J.-Semicarbazide hydrochloride (6.25 g.) was dissolved in 54mls. of 1 N sodium hydroxide and the solution added slowly withstirring, to N-methyl-N- nitroso-N-nitroguanidine (8.2 g.) suspended in50 mls.

of alcohol. The mixture was stirred for 24 hours at room temperature,cooled in ice and filtered. Crystallization from water gave a colorlessproduct, 3.5 g., M.P. 213 C. decomposes.

Compound L.-2 amino 4 hydroxy 6 methyl- 1,3,3a,7-tetrazaindene (3.3 g.,0.02 mole) was dissolved in 85% sulphuric acid (16 g.) and the solutioncooled to C. Absolute nitric acid (1.68 mls., 0.04 mole) was graduallyadded, with stirring, over 10 minutes, keeping the temperature at 0 C.The temperature was allowed to rise to 25 C. and kept there for 1 hour.The resulting solution was poured on ice and the precipitate collected.The product was crystallized from dilute sodium carbonate to give purematerial (2.9 g.) It does not melt.

Compound M.N-itroguanidine (10 g., 0.1 mole) and ethylacetoacetate (13g., 0.1 mole) were refluxed for 4 hours in absolute alcohol (250 ml.)containing sodium (2.3 g., 0.1 mole). The mixture was cooled and theproduct filtered. This sodium salt was dissolved in cold water and thetrace of unreacted nitroguanidine filtered off. The filtrate wasacidified with dilute hydrochloric acid to give the free acid. Twocrystallizations from water gave pure material (6 g.), M.P. 248 C.decomposes.

Compound N. 1,2,4-triazole-3-sulphonamide (3 g.) was gradually added,over 10 minutes, to a mixture of 98% sulphuric acid (15 g.) and absolutenitric (3.6 rnls.) at 010 C. The temperature was allowed to rise to C.and kept there for 1 hour. The mixture was then poured on to 32 g. ofice and cooled to 4 C. overnight. The product was filtered off anddissolved in 5 mls. of water. Addition of about 5 mls, of concentratedhydrochloric acid and cooling gave pure material (1.6 g.), M.P. 187 C.decomposes.

The present invention thus provides a new and useful class ofphotographic silver halide emulsion stabilizer or antifoggant addenda.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention as described hereinabove and as defined in the appendedclaims.

I claim:

1. A photographic silver halide emulsion containing as an antifoggant anitrogen-containing compound having a formula selected from the groupconsisting of and Y-NHNO wherein X is selected from the group consistingof p-toluenesulfonyl, imidazolyl, thiadiazolyl, tetrazaindenyl,triazolyl, thiazolyl, pyrimidinyl and guanidino radicals, and Y is athiadiazolyl radical.

2. A photographic silver halide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaX-NHNO wherein X is a p-toluenesulfonyl radical.

3. A photographic silver halide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaXNHNO wherein X is a imidazolyl group.

4. A photographic silver halide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaX-NHNO wherein X is a thiadiazolyl group.

5. A photographic silver halide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaX--NHNO wherein X is a tetrazaindenyl group.

6. A photographic silver halide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaX-NHNO wherein X is a triazolyl group.

7. A photographic silverhalide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaXNHNO wherein X is a thiazolyl group.

8. A photographic silver halide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaXNHNO wherein X is a pyrimidinyl group.

9. A photographic silver halide emulsion containing about .001 to 10grams per mole of silver halide of an antifoggant having the formulaX-NHNO wherein X is a guanidino group.

10. A photographic gelatino-silver halide emulsion containing about .001to 10 grams per mole of silver halide of an antifoggant having theformula X-NHNO wherein X is a thiadiazolyl group.

11. A photographic gelatino-silver halide emulsion containing about .001to 10 grams per mole of silver halide of3-methylthio-5-nitrosamino-1,2,4-thiadiazole.

12. A photographic gelatino-silver halide emulsion containing about .001to 10 grams per mole of silver halide of 1-nitro-2-nitramino-n-imidazoline.

13. A photographic gelatino-silver halide emulsion containing about .001to 10 grams per mole of silver halide of3-methyl-5-nitramino-1,2,4-thiadiazole.

14. A photographic gelatino-silver halide emulsion containing about .001to 10 grams per mole of silver halide of N-nitro-p-toluenesulphonarnide.

15. A photographic gelatino-silver halide emulsion containing about .001to 10 grams per mole of silver halide of6-methyl-4-nitramino-1,3,3a,7-tetrazaindene.

16. A photographic gelatino-silver halide emulsion conabout .001 to 10grams per mole of silver halide of an antifoggant selected from thegroup consisting of N-nitro-p-toluenesulphonamide,1-nitro-2-nitram.ino-A -imidazoline,3-methyl-5-nitramino-1,2,4-thiadiazole. 3methyl-5-nitramino- 1,2,4-thiadiazole, 6-methyl-4-nitramino-1,3,3a,7-tetrazaindene,3-methyl-5-nitramino-1,2,4-triazole, S-nitramino-l,2,4-thiadiazole,1-acetamido3-nitroguanidine, 1-carbamoyl-4-nitroaminoguanidine,Z-nitramino thiazole, 4hydroxy-6-methyl-2-nitramino-1,3,3a,7-tetrazaindene,4-hydroxy-6-methyl-2-nitraminopyrimidene, and 3- (N-nitrosulphamoyl)-1,2,4-triazole.

17. A photographic emulsion support having coated thereon an emulsion asdescribed in claim 1.

References Cited in the file of this patent UNITED STATES PATENTS2,901,351 Van Pee et al Aug. 25, 1959 FOREIGN PATENTS 835,047 GreatBritain May 18, 1960

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING AS AN ANTIFOGGANT ANITROGEN-CONTAINING COMPOUND HAVING A FORMULA SELECTED FROM THE GROUPCONSISTING OF